The present disclosure relates to delivery systems for implanting transcatheter valves. More particularly, it relates to catheter-based, rapid exchange systems for implanting a stented prosthetic heart valve.
A human heart includes four heart valves that determine the pathway of blood flow through the heart: the mitral valve, the tricuspid valve, the aortic valve, and the pulmonary valve. The mitral and tricuspid valves are atrio-ventricular valves, which are between the atria and the ventricles, while the aortic and pulmonary valves are semilunar valves, which are in the arteries leaving the heart. Ideally, native leaflets of a heart valve move apart from each other when the valve is in an open position, and meet or “coapt” when the valve is in a closed position. Problems that may develop with valves include stenosis in which a valve does not open properly, and/or insufficiency or regurgitation in which a valve does not close properly. Stenosis and insufficiency may occur concomitantly in the same valve. The effects of valvular dysfunction vary, with regurgitation or backflow typically having relatively severe physiological consequences to the patient.
Diseased or otherwise deficient heart valves can be repaired or replaced using a variety of different types of heart valve surgeries. One conventional technique involves an open-heart surgical approach that is conducted under general anesthesia, during which the heart is stopped and blood flow is controlled by a heart-lung bypass machine.
More recently, minimally invasive approaches have been developed to facilitate catheter-based implantation of the valve prosthesis on the beating heart, intending to obviate the need for the use of classical sternotomy and cardiopulmonary bypass. In general terms, an expandable prosthetic valve is compressed about or within a catheter, inserted inside a body lumen of the patient, such as the femoral artery, and delivered to a desired location in the heart.
The heart valve prosthesis employed with catheter-based, or transcatheter, procedures generally includes an expandable multi-level frame or stent that supports a valve structure having a plurality of leaflets. The frame can be contracted during percutaneous transluminal delivery, and expanded upon deployment at or within the native valve. One type of valve stent can be initially provided in an expanded or uncrimped condition, then crimped or compressed about a balloon portion of an inner catheter or inner shaft. The balloon is subsequently inflated to expand and deploy the prosthetic heart valve. With other stented prosthetic heart valve designs, the stent frame is formed to be self-expanding. With these systems, the valved stent is crimped down to a desired size over an inner shaft and held in that compressed state within an outer sheath for transluminal delivery. Retracting the sheath from this valved stent allows the stent to self-expand to a larger diameter, fixating at the native valve site. In more general terms, then, once the prosthetic valve is positioned at the treatment site, for instance within an incompetent native valve, the stent frame structure may be expanded to hold the prosthetic valve firmly in place. One example of a stented prosthetic valve is disclosed in U.S. Pat. No. 5,957,949 to Leonhardt et al., which is incorporated by reference herein in its entirety.
In many transcatheter prosthetic heart valve delivery approaches, a guide wire is utilized to guide the catheter during delivery. The guide wire is preferably made of metal, and is routed through the tortuous path of the patient's vasculature to a desired location at the native valve site. Once the guide wire is in place, the delivery device is advanced over the guide wire and then operated to deploy the prosthetic valve. To accommodate the guide wire, the delivery device incorporates an “over-the-wire” design, forming a central guide wire lumen that extends an entire length of the outer sheath, for example from a distal-most opening in the inner shaft to a proximal opening or exit port at the device's handle. While well-accepted for stented prosthetic heart valve implant procedures, implementation of the over-the-wire approach may give rise to procedural complexities. For example, at least two clinicians are typically needed; one to operate the delivery device via the handle assembly and another to directly manage the guide wire outside of or beyond the handle assembly. Proper guide wire management can become increasingly intricate at various stages of the procedure, due in large part to the significant length of the guide wire outside of the patient. The delivery device is advanced over the pre-placed guide wire by inserting or “back-loading” a proximal end of the guide wire into the distal guide wire port, which in turns leads to the guide wire lumen, of the delivery device. The guide wire thus must be sized such that with the distal end of the guide wire located at the delivery site, a remaining length of guide wire outside of the patient is commensurate with (e.g., at least slightly longer than) a corresponding length of the delivery device, and in particular a length of the guide wire lumen. In other words, the guide wire employed with an over-the-wire system has a length at least double the length of the delivery device's outer sheath. This excessive length requires two clinicians, and increases the time necessary to load or unload the delivery device relative to the guide wire.
Other catheter-based procedures otherwise utilizing one or more guide wires, such as coronary catheter procedures, address some of the over-the-wire concerns by incorporating what is commonly referred to as a “rapid exchange” design. In a rapid exchange system, the guide wire occupies a lumen located only in the distal portion of the catheter. The guide wire exits the catheter through a proximal guide wire port that is located closer to the distal end of the catheter than to its proximal end, and extends in parallel along the outside of the proximal portion of the catheter. The rapid exchange configuration allows for the use of much shorter guide wires (as compared to over-the-wire designs), which enables a single clinician to handle the proximal end of the guide wire at the same time as the catheter at the point of entry into the patient.
Unfortunately, existing rapid exchange technology is not compatible with conventional stented prosthetic heart valve delivery devices. Unlike coronary catheters or other rapid exchange catheters having a single proximal guide wire port, the stented heart valve delivery device would effectively require at least two openings or ports on the proximal side: one in the inner shaft and a second in the outer sheath. In order to load the guide wire into the delivery device, a structured pathway connecting the two proximal side guide wire openings or ports would be necessary. Existing stented heart valve delivery devices do not contemplate rapid exchange, let alone provide requisite design features. Further, the operational requirements of stented heart valve delivery devices (e.g., retraction of the outer sheath relative to the inner shaft and the guide wire when deploying the valve) present distinct design obstacles for the structured pathway to be viable.
Although there have been multiple advances in transcatheter prosthetic heart valves and related delivery systems and techniques, a need exists for heart valve prosthesis delivery systems providing rapid exchange features.